Telephone system.



F. W. DUNBAR.

TELEPHONE SYSTEM.

APPLICATION rum) MAY 9, 1904.

Patented Nov. 24, 1903. 2 SHEETS-SHEET 1.

F. W. D'UNBAR.

TELEPHONE SYSTEM.

APPLICATION FILED MAY 9 1904.

904,850. Patented Nov. 24, 1908.

2 SHEETS-SHEET 2.

UNITED sTArns rr-xrnn'r OFFICE.

FRANCIS W. DUNBAR, Oh CHICAGO, ILLINOlS, ASSIGNCIL TO K ELLOGGSWITCHBOARD AND SUPPLY COMPANY, OF CHICAGO, ILLINOIS, A CORPORA'IION OFILLINOIS.

TELEPHONE SYSTEM.

Specification of Letters Patent.

Patented Nov. 24., 1908.-

Application filed May 9, 1904. Serial No. 206,995.

T 0 all whom it may concern:

Be it known that I, Fnaxols IV. DUNBAR, a citizen of the United Statesof America, and resident of Chicago, in the county of Cook and State ofIllinois, have invented a new and useful Improvement in TelephoneSystems, of which the following is a specification.

My invention relates to improvements in telephone systems, particularlyof the twowire type.

It consists in providing each telephone line with a single relay, whichis preferably polarized and which is suitably actuated by callingcurrent in the line when the subscriber is calling the central oflice,but which is rendered inoperative when the connection is establishedwith the line to retire or prevent the operation of the calling signal.

Other features of the invention include improvements in the cord circuitto adapt it particularly for use with the line circuits.

My invention is illustrated in the accompanying drawings in which Figure1 is a diagram of one form or arrangement of the system, and Figs. 2, 3and i are modifications thereo't'.

Referring particularly to Fig. 1, L and L indicate subscribers linesextending in two limbs 2 and 3 from their respective substations to thecentral. otlice. At the substation A, a call bell 4 and condenser 5 areincluded in a bridge of the line conductors normally closed by theswitch-hook 6; and a receiver '7. transmitter S and retardation coil 9are adapted to be suitably connected in the circuit when the receiver isremoved therefrom. This apparatus is intended to typify any usual ordesired common battery substation outfit. At the central otlice each ofthe lines is provided with an answering jack J and with a suitablenumber of multiple jacks such as J and J all preferably permanentlyconnected with the telephone lines, and with a line relay R whichpolarized by permanent magnet 10. This relay provided with windings 11connected between the tip conductor 2 of the line and conductor 12leading to the positive pole of a battery B which is grounded at thecenter shown by the branch 13. The said relay is also provided withwindings 1 L legged to ground from the sleeve side of the line. Thewindings 11 are so wound that current flowing through them serves toassist the permanent magnet 10 in polarizing the vibrating armature 15of the relay, while the windings 1a are wound so as to produce a northpole upon the free end of one core and a south pole at the free end ofthe other.

These latter windings are therefore the ac-' tive windings of the relay,while the other windings are merely balancing windings for the line andmight be replaced by any suitable windings for that purpose. Thearmature grounded by branch conductor 16 and serves when suitablyactuated. to close the normally open circuit of the line signal S; it ispreferably so adjusted to restore itself so that when unintluenced bythe magnets of the coils, it returns to normal po sition.

Each of the lines is provided with similar apparatus but some of themare connected by a common conductor 12 with a second battery B similarto the battery B. The operators outfit comprises a number of cordcircuits of the type shown in the drawing, each having an answering plug1 and a calling plug P provided with tip and sleeve contact surfacesadapted to register with the corresponding contacts of the spring jacksof the lines when inserted therein. The tip contacts of the two plugsare united by the flexible strands t and f and the condenser 0, whilethe sleeve contacts are connected with flexible strands .s' and s andcondenser 0 The battery I? is bridged across the answering end of thecord circuit and includes upon either side, the supervisory relays r andv controlling, the former through its normally closed contacts and thelatter through its normally open contacts, the local circuit of thesupervisory signal S associated with the answering plug 1. The battery Bis likewise bridged across the calling end of the cord circuit andincludes upon either side of the supervisory relays r and r controllingin a similar manner the local circuit of the supervisory signal Sassociated with the calling plug P. The supervisory relay 9" is providedwith an additional contact 17, adapted in its forward position tocomplete the talking strand t for conversation, and in its normalposition to connect with a grounded high resistance and high impedancetest relay 7", which serves when energized to complete a path forcurrent through the primary of the operators induction coil and theconductors 18 and 12 from the battery B The operators LOU outfit,comprising the usual receiver 19, the secondary of her induction coiland the condenser c is adapted to be bridged across the cord circuit byany suitable listening key 20. it ringing generator is adapted to beconnected between ground and the tip side of the line by means ofringing key springs 21 while at the same time the sleeve of the cordcircuit is connected with the battery lead 23 containing the resistancecoil 2%. The said generator may be connected with the sleeve side of theline by ringing key springs 25, the tip side of the line being at thesame time grounded. Upon the line L two stations are shown with thesignaling bells 4E grounded from the opposite sides of the line.Otherwise the arrangement is the same as that shown at station A.

In the operation of the system the subscriber A removes his receiver andcloses circuit for a portion of the battery B from the positive polethereof over conductor 12, through windings 11 of the line relay R, lineconductor 2, through substation instruments back to the central ofiiceover line conductor 3 and thence through windings 14 of relay R toground and back to the center of the battery. The current through thecoils 14 is now of the proper direction to tip the armature 15 of relayR from its normal position and to close the local circuit of the linesignal S which is lighted to indicate the fact of the call. In responseto the call the operator inserts the answering plug P of her cordcircuit in the jack of the line which permits current from the battery Bto circulate in the metallic line. Current from the positive pole ofsaid battery now flows through the supervisory relay 1 and the windings11 of the line relay R in parallel and thence over the line conductor 2to the substation, returning over line conductor 3. Current also flowsfrom the grounded pole of said battery through the ground and thencethrough the windings 14 of said line relay R to the line conductor 3where it joins the returning current over the telephone line, and flowsover the sleeve strand 8 and through the sleeve relay r to the negativepole of said battery. This current is therefore in the opposite direction through windings 14- of relay R than when the subscriber wascalling the central oflice so that the tongue of said relay is restoredto normal position and the signal S is extinguished. At the same timesleeve supervisory relay r is actuated to close the local circuit ofsupervisory signal S but owing to the fact that tip supervisory relay ris also now actuated the local circuit of said signal is opened and thesignal remains inert.

Connecting her instrument with the line the operator receives the orderand proceeds to test the condition of the wanted line. Normally the testrings of the jacks of the lines are grounded through the windings let ofrelays it and since the tip strand of the cord circuit is groundedthrough the testrelay no flow of current results when the tip of theplug is touched to one of the test rings, and no click is received bythe operator. In case of a connection, however, the said test rings areconnected through the sleeve strand of the cord circuit with thenegative pole of either the battery B or B whereby when the grounded tipof a testing plug is touched to one of the test rings, a flow of currentresults through the test relay and the same is actuated to inductivelycause a click in the ope'rators receiver. It will be understood that thesaid test relay is of suliicient resistance and impedance to prevent alarge or sudden variation of current upon the tested lines so that thesubscribers are not annoyed. Any other test receptive device may, ofcourse, be substituted for the apparatus shown.

Upon finding the line idle the calling plug P is inserted and theringing generator actuated. Closing the springs 21 of the ringing keyserves to connect the generator with the tip side of the line and ringsthe bell at station-D. At the same time current from the lower portionof the battery B flows from ground over conductor 23, sleeve strand 5sleeve conductor of the line acks and through the coils 1st of the linerelay R of the called line, and is in the proper direction to preventits operation. Operating springs 25 of the ringing key would serve toconnect the ringing generator with the sleeve side of the line whichwould operate the call bell at station C, this ringing current isnegative pulsating in character, and the portion flowing through thewindings 14E of relay R serves to maintain the same inoperative.

It will be noted that during ringing, current flows over the conductor12, through windings 11 of relay R and thence over the tip strand of thecord circuit and either through the generator when springs 21 areoperated or directly to ground when springs 25 are operated. In eithercase, however, this current assists the permanent magnet so that thesaid relay is not operated thereby, w iile the retardation of coils 11prevents the passage of the ringing current there through.

After calling the subscriber and before his response relay r is actuatedby current from the negative pole of battery B through said relay andover the sleeve strand 8 of the cord circuit and thence through windings14L of relay R to ground. This current is of suitable direction toprevent the actuation of relay R while serving to energize relay 7 toclose the local circuit of signal S which is now lighted owing to thefact that the subscriber has not yet responded.

Spring 17 of relay r serves now to disconncct the test relay and tocomplete the tip strand of the cord circuit for talking.

Upon the response ol the called subscriber current 'l'lows over the lineL in the same manner as described for the line L so that the relay ractuated to open the local circuit of signal and extinguish the same.

During conversation it is necessary that the direction of the current inthe sleeve winding of the polarized relay should be from ground to thesleeve side of the circuit; in other words, should be the reverse of thedirection of the current when a call is made by a subscriber. If a lineand instrument were of zero resistance, and if the resistance of thesleeve relay .in the cord circuit were 00-0/10 ohms, the windings 11 andll, ot the relay R of 1000 ohms each, and the battery 4-0 volts. then nocurrent would tlow through the sleeve winding of the polarized relaybecause under these conditions the sleeve side of the line circuit andthe ground at the center of the battery would be at the same potential.As, however, the sleeve relay has a resistance higher than 90-0/10 ohms.current will tlow from ground through the sleeve winding to the negativeside of the battery in the cord circuit. This true even it the line andinstrument have zero re 'stance, and the greater the resistance of theline and instrument the greater will be the current tlowing over thispath.

This system of course applicable to one battery in the cord circuit andin practice is perhaps better adapted for such use due to the tact thatvariations between the voltages of the two of batteries may decrease themargin of operation of the system.

Atthe termination of the conversation the subscribers return theirreceivers to the hooks and open the line circuits so that the sameconditions prevail as was described for line L after the subscriber wascalled and before his response. As then pointed out, these relays areprevented from operation so that the line lamps S do not light and sincethe supervisory relays r and r are deprived of operating current thelocal circuits of signals S and S are closed and i the s id lamps arelighted. llpon observing this t e operator withdraws the plug and takesdown the connection, thus restoring all pa ts o normal condition.

in Figs. 3 and t the polarized line relay has but one winding, thebalancing windine; being replaced by a spring contact legged from eitherthe tip or sleeve side of t e circui The polarized relay has thus th enflic s instead of one pair.

In Fig. 2 the batteries B and B are r rd d at the tip end of thebattery. i i c n ers are connected by the conductors 12 and 12 with theactuating windings of line relays R which are connected with the sleevesides of the line circuits. The test relay is therefore connected toconductor 18 leading to the center of the battery instead of to groundas in the former instance. The method of testing, however, is obvious.The tip side of the line is normally grounded through conductor 30.spring 31 of line relay R, the tongue of said relay and ground conductor10. Normally when a subscriber calls, current flows from the battery Bover conductor 12, through the windings of relay R and out over the lineof the substation and thence back to the central 0flice and throughconductor 30, spring 31 and branch 10 to ground. This current is of asuitable direction to actuate the relay R which causes spring 31 toclose the local circuit of the line signal S to light the same. Upon theinsertion of the plug into the jack of the line, the winding of saidrelay R is inclosed in a local circuit with the lower portion of batteryB and is therefore actuated in the reverse direction so as to not onlypermit spring 31 to return to normal position to open the circuit oflamp 5 but to also lift said tongue out of contact with said spring 31,whereby the ground connection from the tip side of the line is opened.This condition is not altered throughout the connection, so that theline signal remains inoperative. Otherwise the operation is similar tothat described with reference to Fig. 1 and will be readily understood.

Fig. 3 shows the line relay permanently connected with the tip side ofthe line. while the sleeve side of the line is normally grounded throughthe tongue of the line relay. The sleeve ends of the batteries B and Bare grounded instead of the tip side as in Fig. 2. This necessitatesringing with negative pulsating current over the tip side oi thetelephone line and with alternating current over the sleeve side of theline. lVhen alternating current is sent over the sleeve side of theline, negative battery is thrown upon the tip side of the line so as tothrow the armature ot' the polarized relay away from the spring contact.The operation is thought to be obvious.

In Fig. 4t the tip side of the circuit is normally connected through thespring contact of the polarized line relay with the negative side of thebattery B lVhen a call is made negative current flows over the tip sideof the circuit through the subscribers instrument. and back through thesleeve windings of the polarized relay to ground. This establishes anorth pole on one core of the relay and a south pole on the other coreso that the armature will be suitably attracted to close the line lampto ground, thus lighting it. lVhen the call is answered positive currentwill be sent through the sleeve relay in the cord circuit and throughthe winding of the polarized relay to ground. This will attract thearmature of the polarized relay in the opposite direction, first openingthe line circuit and then the tap from the tip side of the line to thearmature of the relay. The spring contact is prevented from followingthe armature by the dead stop 32 as shown in this figure as well as inFigs. 2 and 3. In the case of Fig. 4, if the line and instrument were ofzero resistance, no current would flow through the line relay, but asthe line and instrument always have some resistance positive currentwill flow through the windcases. It is obvious that in plugging into acalled for line the polarized relay will be operated in a direction tocut-oii the tap from the tip side 01": the cord circuit. In thisinstance again the batteries are grounded at the center.

It will be understood that the several grounds mentioned may be and inpractice usually are one and the same or they may be the common officereturn and that the ringing and listening keys mentioned may be any ofthe usual types.

Having thus described my invention, what I claim and desire to secure byLetters Patent is 1. In a telephone system, the combination with atelephone line, of a polarized line signaling device connected therewithat the central office, a source of current connected with the line atthe central office and adapted to send current through said device inthe proper direction to operate the same when the subscriber is calling,a cord circuit at the central office to establish connections with theline for conversation, a pair of electro-magnets one associated witheach limb of the cord circuit, a supervisory signal controlled by saidmagnets, one of said magnets being included in a local circuit with theactuating windings of said device when a connection is established withthe line, the current in said local circuit being in the properdirection to render said device inoperative and sufficient to energizethe magnet to cause said supervisory signal to operate and the othermagnet being placed under the control of the subscriber and serving whenenergized to render the supervisory signal inoperative, substantially asdescribed.

2. In a telephone system, the combination with a telephone line, of apolarized line signaling device connected therewith at the centraloflice, a central source of current in said line adapted to send currentthrough the said device in the proper direction to operate the same whenthe subscriber is calling, a cord circuit at the central office toestablish connection with the line for conversation, a pair ofelectro-magnets associated with said cord circuit, a supervisory signalcontrolled thereing of the polarized relay to ground in all.

by one of said magnets being connected in a local circuit with saiddevice and including a portion of one of the talking strands of the cordcircuit when a connection is established with the line, the current insaid local circuit being the proper direction to render said deviceinoperative and of sufficient strength to cause said supervisory signalto operate, and the other electromagnet being in the path of currentover a portion of the other talking strand of the cord circuit and themetallic telephone line and therefore under the control of thesubscriber, said electromagnet serving when energized to render saidsupervisory signal inoperative, substantially as described.

In a telephone system, the combination with a telephone line, of apolarized line signaling device connected therewith at the centraloffice, a source of current connected with the line at the centraloffice and adapted to send current through said device in the properdirection to operate the same when the subscriber is calling the centraloffice, a cord circuit to establish connections with the line forconversation, a pair of relays associated with the cord circuit, asupervlsory signal controlled by said relays, one of said relays beingincluded in a local circuit with said device completed over a strand ofthe cord circuit when a connection is established with the line, thecurrent in said local circuit being in the proper direction to rendersaid device inoperative and of sufficient strength to operate said relayto cause said supervisory signal to operate, and the other being in thepath of current completed over another strand of the cord circuit andover the metallic line whereby it is under the control of thesubscriber, said latter relay serving when actuated to render saidsupervisory signal inoperative, substantially as described.

I. In a telephone system, the combination with a telephone line, of apolarized line signaling device connected in the metallic circuitthereof at the central office, a source of current connected with theline at the central office and adapted to send current over the metallicline and through said device in the proper direction to operate the samewhen the subscriber is calling, a cord circuit to establish connectionwith the line for conversation, a pair of signal controllingelectro-magnets associated with the cord circuit, a supervisory signalcontrolled thereby, one of said magnets being included in a localcircuit with the said device completed over a strand of the cord circuitwhen a connection is established with the line, the current in saidlocal circuit being in the proper direction to render said deviceinoperative and of sufficient strength to operate said magnet to causesaid supervisory signal to operate, and the other magnet being includedin the path of current over another strand of the cord circuit and themetallic line and placed under the control of the subscriber, saidlatter magnet serving when energized to render said signal inoperative,substantially as described.

5. In a telephone system, the combination with a telephone line, of asignaling device therefor at the central office having a coil in eachlimb of the telephone line and normally under the control of thesubscriber, a cord circuit to establish connections with the line forconversational purposes, a source of current associated with the cordcircuit, and supervisory apparatus connected with the cord circuit, saidsignaling device being actuated by current in one direction when thesubscriber is calling, and being rendered inert by current in theopposite direction when a connection is established with the line forconversation, substantially as described.

6. In a telephone system, the combination with a telephone line, of apolarized line signaling device at the central office, a cord circuit toconnect with said line, a pair of supervisory relays and a source ofcurrent in a bridge of the cord circuit, one of said relays beingadapted to be actuated over a local circuit including the polarized linesignaling device when the cord is connected with a line, the other ofsaid relays being under the control of the subscriber, and a supervisorysignal controlled by the conjoint action of said relays, substantiallyas described.

7 In a telephone system, the combination with a telephone line, of apolarized line signaling device therefor at the central oflice actuatedto display its signal when a calling line is closed at the substation, acord circuit to connect with the line, a pair of supervisory relays in abridge of said cord circuit, one of said relays being placed in a localcircuit including a coil of said line signaling device when the cord isconnected with the line, whereby said line signaling device isdifferently actuated to efi'ace its signal, the other of said relaysbeing placed in a circuit under the control of the subscriber andcornpleted through the contacts of the subscribers instrument, and asupervisory signal controlled by the conjoint action of said rclays,substantially as described.

8. In a telephone system, the combination with a telephone line, of acord circuit to connect therewith for conversation, a pair ofsupervisory relays, and a source of current in a bridge of said cordcircuit, a conductor connected with an intermediate point of saidsource, a line signaling device for the line, said line signaling deviceand one of said supervisory relays being actuated over a circuitincluding said conductor when the cord is connected with a line open atthe substation without displaying the line signal, a supervisory signaldisplayed by the actuation of said latter relay, the other of saidsupervisory relays being actuated over the telephone line when the lineis closed at the substation, said latter relay being adapted to eflacesaid supervisory signal, substantially as described.

9. In a telephone system, the combination with a telephone line, of apolarized line signal therefor having a coil in each strand of thetelephone line, a central source of current, a portion of said sourcebeing adapted to furnish current to the telephone line through the coilsof said line signaling device, current from said portion of the sourcebeing adapted to energize said polarized line signaling device in theproper manner to display the signal when the line is closed at thesubstation, a cord circuit, means to reverse the current through aportion of said polarized line signaling device when the cord isconnected with the line, whereby the device is difi'erently actuated toeflace the line signal, substantially as described.

Signed by me at Chicago, county of Cook, State of Illinois, this secondday of May FRANCIS V. DUNBAR. lVitnesses:

GAZELLE BEDER, L. D. KELLoee.

